1. Field of Invention
This invention relates to a ladder for use on land conveyances which automatically returns to an original position after impact with grade or objects.
2. Description of the Related Art
A ladder is frequently used on a land conveyance, such as a dump truck, to allow access to the payload area from the ground. The ladder is removed or retracted above the truck during movement of the vehicle. Typically the ladder is removed by hand or by applied pressure to a mechanical device. Conventional ladders have the disadvantage that the structure can become bent if the ladder is not removed during moment of the vehicle or if another vehicle contacts the ladder during use. Also, the release mechanism can malfunction resulting in inoperability of the ladder. Without a ladder, the operator has either an unsafe access to the payload area or no access at all. The operator can either ascent or descend the vehicle on a bent or out of position ladder or on the vehicle itself or simply leap off the vehicle. The above alternatives often result in accidents to the operator. The problem of providing a permanent ladder for a land conveyance which is able to withstand considerable impact has persisted since the initial use of ladders on land conveyances.
A typical self-storing ladder for a vehicle is described in U.S. Pat. No. 4,161,997. In this assembly, a step section is pivotally mounted to a vehicle. Pivoted pins are aligned in bores to effect the desired pivotal connections. The step section is manually pivoted about a horizontal axis between an operative position and a storage position. When the ladder is in use, the ladder is anchored to the ground with a foot plate attached with wing bolts. The ladder is moved into the storage position by loosening the wing bolts and pivotally rotating the ladder.
U.S. Pat. No. 5,024,292 to Gilbreath et al. describes a ladder mountable to a column in order to swing laterally about the column and to be tilted in vertical planes. A spring is arranged to bias the ladder after being moved to a predetermined position.
U.S. Pat. No. 5,064,023 to Loeber describes a flexible ladder for use on a moving vehicle which provides frontal stability but lateral flexibility. A first set of steps are fixedly attached to the vehicle. A second set of steps are attached to the vehicle below the first set of steps. Three rubber struts are used to mount the second set of steps to the vehicle. Metal straps are attached to the rubber struts to increase the frontal stiffness of the ladder.
Of possible general relevance to the invention are U.S. Pat. Nos.: 2,164,327, 3,882,965, 4,121,495, and 4,753,447 which describe assemblies for portable ladders.
A practical solution for an automatically returning ladder assembly is not found in the prior art.